Positive or Negative Earth?

[SpitNoir]

Greetings all. Have an "issue" with a '65 Spitfire's wiring I could use some help with. Namely, now do I tell if a system has been converted from one to the other?
Car should be a Positive Earth car (if my info is correct), but the battery has been disconnected for years and the cables don't fit their respective battery posts/terminals as one would presume.
The clamp on the Negative side (black cable to starter solenoid) is quite a bit larger than the battery post and will not clamp down at all. The Positive cable's (short Red one to Earth) clamp is way too small to even fit over the larger positive battery post.
So evidently, this car has been run previously with the battery hooked up "backwards" with seemingly no ill effects that I can see. The car ran before it was put in a body shop 7 years ago (yeah, I know, another story in itself), and the owner just doesn't remember those things that far back. And even though the body shop could have tried hooking up the battery and got it wrong, it doesn't appear that anyone's done this recently.

So my questions are, again:
1. How can I tell if it's still meant to run as a Positive Earth?
2. How can I test it without damaging anything. And...
3. Is there really anything that can be damaged (generator/dynamo, instruments, etc.) if I hook it up to Negative Earth and give it a shot?

Thanks for any help. I did a search and came up with zip. Perused the first 41 pages here (not boring, but not quick!) and didn't find any discussions of Positive Earth cars.

Sorry for the long-winded post. I get that way when I'm having fun.
Which is most of the time!

Thanks again.

Paul

[SpitNoir]

Oops, just realized as I was browsing, that this might have been more appropriately posted over in the Technical Chit Chat category. Thought about that last night, but by daylight, all had been forgotten.
If that's correct, perhaps one of the moderators/admins can move it on over.

Paul

[herald948]

With the possible exception of a radio that might have been fitted, nothing would've been harmed -- nor will be harmed now -- by reversing the polarity!

[redzer]

Could it kill the Alternator if it has been converted from dynamo to an alternator in the past,
i managed to switch the polarity on my later spit which is another story, it started ok unfortunately because it blew the fuse in the radio and killed the alternator  :(

[SpitNoir]

Thanks for the replies. Good to know. So now I can just hook it up the way it makes the most sense and test things from there. it's still got the original (or a reasonable facsimile thereof) generator, so no alternator to fry.
It does however, have a newer radio/CD player in it, so I'll be cautious and at least check it's connections, if not completely disconnecting that first. It's a model I don't recognize from Mitsubishi, so I wonder if it was purchased as a positive earth model? I'll dig deeper into that mystery, but for now I just want to get the lights re-deployed and get it running.
Joy.
Sorry to hear about your ex-alternator redzer. Did that to a Corvair with an updated (internally regulated Delco) alt not long ago (long after I knew better), and for some reason it didn't seem to hurt anything. Lucky day that.

Thanks again.

Paul

[1967 MkIII]

Hi all, jumping in here with my own question

I got hold of a radio with a switch for both +ve & -ve earth, but how can I check what the Spitfire is? What where they originally?

An alternator has been fitted (by PO). Couple of pics below. Which might not help at all, but who doesn't enjoy seeing a Triumph engine?  ;D

Thanks for any help

[willcolumbine]

Nice car! That's negative earth. All you need to do to tell is to follow the cable from the negative battery terminal. If it goes to the bodywork then it's negative earth!

[heraldcoupe]

If it's got an alternator, the chances of it being positive earth are very small indeed. While there was a positive earth alternator kit offered as an official upgrade, they are very, very scarce. Anything likely to have been fitted in more recent times will have made a negative earth conversion essential. Likewise, if a modern stereo is fitted, it will be have to be insulated from the body (including the aerial) to work with a positive earth electrical system.

With a dynamo equipped vehicle there's little consequence to swapping polarities. The heater motor is the only item which is dependant on polarity. Being a centrifugal blower, it will still flow inthe same direction, but the vanes are optimised to blow mre efficiently in one direction than the other, so if spinning backwards, airflow is reduced,

Cheers,
Bill.

[drofgum]

Bill,
Don't the Spitfire and Gt6 blower motors have field windings? If they do then reversing polarity won't reverse the blower: both the field and the armature will be reversed, so, the motor will still run the same direction. Permanent magnet motors do reverse when you change polarity because the field from the magnet stays as it was, but the armature is reversed.
                                                                                                             Cheers,
                                                                                                             Paul

[SpitNoir]

What they said. Including the "very nice" comments!
I'm pretty sure the official change-over was during the '67 model year anyway, but not sure at what serial number that happened. From all their comments though, I'd think you're good with that information.

One thing I notice though (with mine as well) is that your ground cable is a simple braided model with only the one mounting point. That seems to work acceptably well, in most cases (from what I've seen anyway), but in catalogs I've seen that show original cables, the factory had a longer one with attachment points at both the body and the engine block. Since the starter is the single largest user of current (albeit usually only momentarily) it makes sense to have a direct path to the battery negative as close to the starter motor as is reasonable. I always have multiple ground paths on vehicles I wire up and it's served well.
At least that's how they show it for a MkI. Anyone out there still sporting a factory original battery-earth cable? Or a copy thereof?

PaulB

[piman]

Hello Paul,

have a look at the coil connections, if the distributor wire (white\black) is on the - ve then it probably was negative earth (which is likely with a modern radio)? Which ever way you decide make sure the coil polarity is correct, with the distributor connection the same as the battery earth connection.

Alec

[heraldcoupe]

1317 wrote:

Bill,
Don't the Spitfire and Gt6 blower motors have field windings?

I don't have one to hand for test purposes, but most of the other Triumph (Smiths & Delaney) blower motors use permanent magnets.

Cheers,
Bill.

[1967 MkIII]

Thanks for your quick responses gents, much appreciated along with the kind comments.

PaulB, would you then run a few wires from the negative terminal to the bodywork & engine? They would need to be against bare metal of course?

I'll need to check the heater blower as it's very weak. I assumed it was just the nature of the car :)

Steve

[willcolumbine]

2057 wrote:

PaulB, would you then run a few wires from the negative terminal to the bodywork & engine? They would need to be against bare metal of course?

The standard arrangement is a braided strap running from the negative terminal to the point on the bodywork where yours attaches and then following the line of the loom down to bolt up with one of the bellhousing bolts near the starter.

[SpitNoir]

What he said.
Should be reasonably easy to find a pre-terminated cable of the proper length to do just that. If you go stranded cable instead of braided, for that minimal length I would think anything 6-gauge or larger would do the trick. Even on small and easy-to-start engines, I prefer 4ga or larger, just in case of extended starting scenarios. After all, sometimes overkill is just enough!
And just because I can...

Paul

[SpitNoir]

piman wrote:

...if the distributor wire (white\black) is on the - ve then it probably was negative earth (which is likely with a modern radio)?n.

Alec

Hi Alec. Great advice! Simple, and I should have thought of it myself. I think I did actually, but about a nanosecond later was off on another tangent. I like to think so anyway!
With that in mind, I did check them out. Problem is with this blue colored Bosch coil (original or replacement?) the indicators are "1" and "6" which don't mean anything to me. I haven't checked out any Bosch technical info yet though, so I'll do that next.
Any idea what the numbers might mean with regard to positive and negative?

Thanks again. Sorry it took me so long to act on your advice. Been avoiding the car like the plague. So to speak...

Paul

[drofgum]

Paul,
I found( http://bmwmotorcycletech.info/wires&codes.htm ). Which lists the common numbers used on newer European wiring parts. That page also refers to other pages with more information on these numbers.
                                                                            Cheers,
                                                                            Paul

[SpitNoir]

Perfect! Thanks for that link. Double-checked myself, and the numbers on the coil were "1" and "15", so now I can verify which way it's hooked up. Tomorrow, in the daylight.

I did find some info tonight though, that pretty much clinches it for me. While delving into John Thomason's "Guide to Originality" and looking for possible locations of side-view mirrors and other stuff, I chanced upon some electrical info in the Mark III specifications. At the bottom of the page was a special note attached to the electrical info which states that the changeover from positive to negative earth actually occurred sometime in '64, rather than the previously thought of '67 model year!!!
Too bad that there is no such specification page for the Mark I or II, and no wiring diagrams for the pre-'67 cars in the BGB (Big Green Book) that I've been using for reference.
Both books are well put together I feel, so the relative lack of early info may be due to the info just not being as well documented. Sounds plausible at least?

So anyway, I think I can be reasonably certain that this car, being from late '64, was probably negative ground as delivered after all. Which would explain a lot!
Still, I'm going to verify the coil connections. before moving on to the next mystery.

Thanks again to all.

Paul

[SpitNoir]

The plot thickens...
In the way of an update, the coil actually was wired as if in a positive ground system. Sound like someone thought, just as I did, that all the early models were positive ground and hooked it up this way even though the battery connections indicated otherwise.
Still, it did put out enough spark to light the engine. Going to swap wires tomorrow and hope for an even better spark. Naturally, there is a fuel problem to deal with first though.

PaulB

[wheels2014]

I had a 65 spit & it was positive earth. I installed a neg earth radio which i insulated, but unfortunately the insulation wore thru & I ended up having to replace most of the melted dash wiring!